The present invention relates to an airbag apparatus that inflates and deploys an airbag in a space between a vehicle body side portion and a vehicle seat when an impact is applied from a side of the vehicle, thereby attenuating the impact.
As means for protecting an occupant from an impact that is applied to a vehicle from a side due to a side collision, side airbag apparatuses widely known. FIGS. 18 to 21 show one such side airbag apparatus having an inflator 101 and an airbag 102. The airbag 102 is formed by laying a pair of fabric main portions 103 in the direction of the width of the vehicle and sewing the fabric main portions 103 together at joint portion 104 at peripheral portions. The inflator 101 is located in a rear section inside the airbag 102. After being folded into a compact form, the airbag 102, together with the inflator 101, is incorporated in a backrest 117 of a vehicle seat 116 (refer to FIG. 18). In such a side airbag apparatus, when an impact is applied from the side of a body side portion of the vehicle such as a side door, the inflator 101 jets inflation gas G into the airbag 102. The jetted inflation gas G inflates and deploys the airbag 102 toward the front of the vehicle from the backrest 117 into a narrow space between an occupant P seated in the vehicle seat 116 and the body side portion. This attenuates the impact that is transmitted from the side to the occupant P through the body side portion.
In accordance with the above described airbag apparatus, to reduce the influence of heat and pressure of the inflation gas G on a part of the airbag 102 in the vicinity of the inflator 101, reinforcing fabric sheets 105, 106 are sewn to the inner sides of the fabric main portions 103 at joint portions 107, 108 (see Japanese Laid-Open Patent Publication No. 2007-186132). Side portions 106S of the reinforcing fabric sheet 106 are folded back so that parts having multiple layers are formed in the reinforcing fabric sheet 106 (see FIGS. 19 and 20).
Representative examples of parts to be reinforced by the reinforcing fabric sheets 105, 106 include parts in the vicinity of gas outlet 101A of the inflator 101, that is rear parts of the airbag 102.
In the side of the human body, lumbar regions are known to have a better impact resistance than the thorax and abdomen. Therefore, when the airbag 102 is inflated and deployed, and pushes an arm PA of the occupant P inward in the width direction of the vehicle, the arm PA is likely to push the thorax and abdomen PB, which have relatively low impact resistance.
Accordingly, the airbag 102 is provided with an annular inflation limiting portion 109 at a position corresponding to the arm PA of the occupant P (refer to Japanese Laid-Open Patent Publication No. 2007-186132 and Japanese Laid-Open Patent Publication No. 2005-053465). The inflation limiting portion 109 is formed by sewing the fabric main portions 103 to each other at a position corresponding to the arm PA of the occupant P, while placing the fabric main portions 103 close to each other. According to the side airbag apparatus having the inflation limiting portion 109, the thickness of the airbag 102 along the vehicle width at the time when the airbag 102 is inflated and deployed is limited in a region where the inflation limiting portion 109 is provided. Accordingly, the arm PA is less likely to be pushed inward along the vehicle width direction by the airbag 102 and press the thorax and the abdomen PB.
Being located at a position forward of the gas outlet 101A of the inflator 101, the inflation limiting portion 109 is susceptible to heat and pressure of the inflation gas G. Accordingly, the inflation limiting portion 109 is also reinforced by the reinforcing fabric sheets 110. The reinforcement by the reinforcing fabric sheets 110 is executed by placing the reinforcing fabric sheets 110 at positions that are inside of the fabric main portions 103 and correspond to the arm PA of the occupant P. The reinforcing fabric sheets 110 are sewn to the fabric main portions 103 at joint portions 111. Accordingly, the reinforcing fabric sheets 110 and the fabric main portions 103 located outside of the reinforcing fabrics 110 are sewn together by the inflation limiting portion 109. Sewing threads used for forming the inflation limiting portion 109 have higher strength against heat and pressure than the sewing threads for forming the joint portions 111.
Further, the peripheral portions of the fabric main portions 103 may be reinforced by upper and lower reinforcing fabric sheets 112, 113. The upper and lower reinforcing fabric sheets 112, 113 are sewn to the peripheral portions of the fabric main portions 103 by joint portions 114.
However, when the separate reinforcing fabric sheets 105, 106, 110, 112, 113 are used for different parts to be reinforced, the number of reinforcing fabric sheets is increased. Accordingly, when joining the reinforcing fabric sheets 105, 106, 110, 112, 113 to the airbag 102, the reinforcing fabric sheets 105, 106, 110, 112, 113 need to be placed one by one on the corresponding parts of the fabric main portions 103 to be reinforced. Thus, the arrangement is troublesome and takes a long time.
Although providing the different reinforcing fabric sheets 105, 106, 110, 112, 113 for different parts to be reinforced reduces the influence of heat and pressure of the inflation gas G on each part of the airbag 102, particularly, on the joint portions 104, 107 to 109, and 111, there is still room for improvement. Specifically, the inflation gas G, which is jetted forward from the inflator 101, separates the rear edge of each reinforcing fabric sheet 110 from the fabric main portion 103 located adjacent to and outside of the reinforcing fabric sheet 110, and enters the gap created by the separation. In such a case, the inflation gas G is likely to stay in the gap after hitting the rear section of the joint portion 111 in the gap. As this phenomenon continues, the rear section of the joint portion 111 is influenced by the pressure and heat of the inflation gas G. Accordingly, holes in the reinforcing fabric sheets 110 and the fabric main portions 103 in the joint portion 111, through which sewing threads are passed, are enlarged. In other words, enlarged apertures appear. Particularly, as the costs for the inflator 101 have been reduced in recent years, the temperature of the inflation gas G tends to be increased. The use of the inflator 101 increases the above described influence.
To deal with the above described phenomenon, the present inventors have concluded that it is effective to use a single long slender reinforcing fabric sheet extending in the front-rear direction to reinforce parts to be reinforced that are adjacent to each other in the front-rear direction, particularly parts in the vicinity of the inflator and parts in the vicinity of the inflation limiting portion. In this case, arranging the single reinforcing fabric sheet allows a plurality of parts to be reinforced at a time. This reduces the steps for arranging multiple reinforcing fabric sheets. However, it has been found that this will cause other problems. That is, since the reinforcing fabric sheet has a long slender shape, parts of the fabric main portions where the reinforcing fabric sheets are provided are harder to stretch and inflate than parts where the reinforcing fabric sheets are not provided. In the fabric main portions, the amount of stretch (inflation amount) is significantly different between parts with a reinforcing fabric sheet and parts without a reinforcing fabric sheet. Therefore, the reinforcing fabric sheet greatly influences the deployment of the fabric main portions. Therefore, when being deployed, the airbag behaves in a different manner from the above described conventional airbag 102, in which the different reinforcing fabric sheets 105, 106, 110, 112, 113 are provided for reinforcing different parts. As a result, such an airbag may be unable to achieve deployment performance (for example, the speed of deployment) equivalent to that of the conventional airbag 102.